As a general principle of railcar design and operation it is advantageous to maximize the ratio of gross (fully loaded) car weight to light (empty) car weight, so that effort expended to drive a train is used to move freight, rather than merely to move the weight of the railcars. This can be done in three ways. First, the weight of the load can be increased, up to a regulated limit. Second, the weight of the railcar can be reduced. Third, the versatility of the railcar can be improved so that it spends less time rolling empty or partially empty. In applying this principle to automobile carrying railcars, improvements in the versatility of stacking more than one layer of automobiles per car and in reducing railcar weight tend to improve energy efficiency per unit of weight carried.
Railcars have long been used to carry automobiles. An early method was to carry automobiles or trucks on standard flat cars. In the flatcar type of design, the automobiles were loaded on a flat deck, and the main fore-and-aft structural member of the railcar was a centre sill. Automobiles are a relatively low density load, unlikely to reach the railcar lading limits. Consequently, from at least as early as U.S. Pat. No. 1,229,374 issued Jun. 12, 1917 to Youngblood, attempts have been made to stack vehicles, and thereby increase the load carried by each railcar.
One way to allow higher stacking was to use a centre-depressed railcar as shown in U.S. Pat. No. 1,894,534 issued Oct. 9, 1931 to Dolan, in which the main fore-and-aft structural members, a pair of side sills, drop down between the railcar trucks. Dolan employed individual stacking units for each automobile lifted. Youngblood used a full length lifting deck which permitted two loading configurations--a lowered position, and a raised position.
Youngblood shows a lifting structure installed on an existing car and surrounded by box car sides. Later designs show a flatcar deck and spaced apart vertical stanchions from which the automobile decks are suspended. This kind of flat-car with stanchion structure is shown, for example, in U.S. Pat. No. 3,119,350 issued Jan. 28, 1964 to Bellingher; U.S. Pat. No. 3,205,836 issued Sep. 14, 1965 to Wojcikowski; U.S. Pat. No. 3,221,669 issued Dec. 7, 1965 to Baker et al., U.S. Pat. No. 3,240,167 issued Mar. 15, 1966 to Podesta et al.; and U.S. Pat. No. 3,547,049 issued Dec. 15, 1970 to Sanders. The full length, flat deck tri-level style of auto carrier became, and remains, the industry standard.
Triple deck cars are typically designed to carry about a dozen automobiles over railcar truck centres of 55 to 60 feet and unit length of about 70 feet, or fifteen to eighteen cars on railcar truck centres of 64 to 70 foot centres on a railcar having a total main deck length of about 90 feet. For an average automobile weight of about 2000 Lbs., this gives a load in the range of 24,000 Lbs/70 feet (roughly 350 Lbs/ft) to 36,000 Lbs/90 feet (roughly 400 Lbs/ft). Yet a standard flatcar is designed to carry 100,000 Lbs (roughly 1000-1300 Lbs/feet). Thus the basic flat car structure has much greater capacity than is required for the load.
In one currently used design, the flatcar weighs roughly 60,000 Lbs, and the automobile supporting superstructure weighs more than 32,000 Lbs, for a total of 92,000 Lbs. For an automobile load of 30,000 Lbs., roughly three quarters of the hauling effort is expended to move the railcars. And, on the return journey the cars may be empty.
In a traditional railcar the bending moment due to the vertical load is carried in a fully extending longitudinal centre sill. In one example sill dimensions were roughly as follows: (a) Overall Height--30" (b) Top Flange Effective Width--40" (+/-) (c) Top Flange Thickness 0.375" (d) Bottom Flange Width--30" (e) Bottom Flange Thickness--0.625" (f) Web Thickness 0.3125". The centre sill, by itself, had an effective cross sectional area of about 59 in sq. Typical side sills for such a car each had a depth of about 14", a cross-sectional area of 8.5 in.sq., giving an overall area of about 76 in.sq. Put in other terms, a cross sectional area of 76 in sq. is roughly equivalent to a sectional weight of slightly over 250 Lbs. per lineal foot. A cross sectional area of 30 inches similarly corresponds to just over 100 Lbs. per lineal foot. The second moment of area of the centre sill was about 9600 in.sup.4 , the local second moment of area of each of the side sills was about 240 in.sup.4. For a car having a main deck at 38 inches above top of rail (TOR) the effective neutral axis of the structure was about 24 inches above TOR and the effective second moment of area was about 11,900 in.sup.4. The flat car was designed for a 200,000 Lb maximum load, rather than a 30 to 40,000 Lb load.
One way to reduce the weight of the rail-car is to minimize, or to do away with, the main sill. To that end, an automobile carrier having an integrated load bearing roof structure permits a reduction in the size and weight of the main sills. The bending moment due to the load and due to the railcar's own weight can be carried in a truss having an effective depth roughly equal to the height of the railcar itself For a flat decked car, removal of all but the end portions of the centre sill presents an opportunity to save several thousands of pounds of weight. Consequential weight savings--from the removal of ancillary cross beams and the use of correspondingly lighter upper structure, may permit additional weight savings.
Automobile carriers, having had a long historical descent from flat cars, have not had substantial roof structures. Coverings, if used at all, have tended to be supported on the tops of the vertical stanchions, and have tended to involve only secondary or tertiary structural support. The primary structural members have remained the longitudinal main sills at the main deck level, whether along the centre of the car, or as large side sills on centre-depressed cars or well cars.
A railcar can be idealized as a beam simply supported at, or near, its ends by a pair of railcar trucks. The span of the beam is typically 60 to 75 feet. It must withstand longitudinal loads in tension and compression, and longitudinally distributed loads acting vertically causing the beam to bend. Design is limited by the yield stress of the material at the point of maximum bending moment. For a known maximum load distribution, the maximum stress in the material is reduced when the second moment of area of the structure is large and when a relatively larger share of the material of the section is concentrated far from the neutral axis of the section. Use of a deep section with well spaced flanges is likely to permit a smaller quantity of material to be used to carry the same load. Thus, not only does the removal of the centre sill promise a reduction in weight, but by using a truss and so deepening the beam, there is an opportunity to reduce the thickness of the remaining material.
Another way to reduce the weight of an automobile carrier is to reduce the number of trucks. To that end, an articulated car of several units, whether 3 or 5, or some other number, would save considerable weight over the older style cars. Articulation is suitable too, given the convenience of being able to drive from one rail-car to the next when loading automobiles.
It remains to consider the versatility of existing automobile carrier designs. Wojcikowski used three decks running the entire length of the car, those decks being movable to the desired heights for carrying cars. U.S. Pat. No. 3,221,669 issued Dec. 7, 1965 shows another kind of adjustable tri-level full-length deck car. Another tri-level car, with fixed height decks is shown in U.S. Pat. No. 3,240,167 issued Feb. 27, 1961 to Podesta et al., has gangplanks to permit automobiles to be driven from one railcar to the next in a multi-car train, thus simplifying loading.
It is advantageous to be able to carry different heights of vehicles on one train, or to be able to convert from a three level train, for carrying sedans, to a two level train, for carrying utility vehicles, for example, since this may allow an operator to reduce the amount of empty, or less than full, operation.
According to the American Association of Railroads standards, the lower deck of a bi-level car should be located 3'-81/2" above the top of the rail for a new railcar. The upper deck should have a minimum clearance of 7' 3" above the lower deck, and a maximum height of 11' 3" above the rail. The roof structure should have a minimum clearance of 7' 91/4" above the upper deck, and the overall railcar height at the railcar centre line should not exceed 19'-1".
Similarly, the deck heights for a tri-level car require that (a) the lowest deck be 2' 71/2" above rail; (b) the middle deck be 8'-011/16" above rail, with a minimum clearance of 5' 23/8" above the lowest deck; (c) the top deck be 13'-43/8" above rail, with a minimum clearance of 5'-17/8" above the middle deck; and (d) the maximum railcar height at centre line is 19'-1" with at least 5'-511/16" clearance above the top deck.
It can be seen from these dimensions that the difference in dimensions between the upper deck of a bi-level configuration and the top deck of a tri-level configuration is, ideally, 253/8". Similarly, the difference in dimension between the upper deck of a bi-level configuration and the middle deck of a tri-level configuration is 385/16". Given these differences in heights, it would be advantageous to have a deck adjusting system capable of moving the top and middle decks through unequal distances.
Notably, the standard triple deck automobile carrier uses straight-through flat decks. In a fixed deck system it would not offer a stacking advantage to use a depressed centre main deck, since the maximum lower deck vehicle height would generally be determined by the second deck clearance above the end structure shear plate mounted over the railcar trucks.
Removal of the central section of the main sill, leaving only stub sills at the ends of the car permits the use of a depressed centre car, but with a continuous deck for end loading, rather than individual loading. A moveable second deck may be raised to permit, for example, one or two family vans to be loaded in the space permitted in the low central section, while sedans, or sports cars, are loaded over the end structure shear plates. The second deck may then be lowered to its loading position once the vans are in place. It is advantageous for such a loading system to be operable on relatively short notice, and for it to operate relatively quickly when required. It would also be advantageous for that system to be operable by a singe operator. A positively driven system for forcing the decks into position, as opposed to a gravity dependent system, is considered advantageous by the present inventors.